Bonded textile materials



y 2, 1970 5. DAVIES 3,511,747

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U.S. or. 161-150 United States Patent 3,511,747 BONDED TEXTILE MATERIALSStanley Davies, Pontypool, England, assignor to British Nylon SpinnersLimited, Pontypool, England, a corporation of Great BritainContinuation-impart of application Ser- No. 346,752, Feb. 24, 1964. Thisapplication Aug. 13, 1968, Ser. No. 752,389 Claims priority, applicationGreat Britain, Mar. 1, 1963, 8,209/63 Int. Cl. D04h 1/04 16 ClaimsABSTRACT OF THE DISCLOSURE A bonded textile material containing fibresconsisting of' at least two fibre forming synthetic polymer componentsarranged in distinct zones across the cross-section of each fiber, atleast one, but not all of which components are potentially adhesive andlocated on at least a portion of the'periphelal surface thereof. Thefibers are bonded by the adhesive material, but do not form crirnpsduring the formation of the mat due to the application of pressureduring bonding.

This application is a continuation-in-part of U.S. application Ser. No.346,752, filed Feb.'24, 1964, now abandoned.

Thisinvention relates to bonded fibrous materials and more particularlyto fibrous materials which are bonded together by the. adhesivecharacteristics of at least a proportion of their constituent fibres.

It has already been proposed to adhesively bond fibrous materials byincorporating homogeneous binder fibres in the materials, the binderfibres generally being rendered adhesive by the action of heat or asolvent. However, when such fibres are rendered adhesive underconditions such as to obtain a product having adequate strength, theylose their fibrous form and the adhesive spreads through the structure,rendering the materials stiff and conferring on "advantages'as thosebonded with homogeneous binder fibres. Frequently thermosetting resinshave been used as the coating material and these resins produce evenstiifer and harsher materials since the thermosetting resins polymeriseto a hard brittle infusible mass. Further disadvantages resulting fromthe use of fibres coated with a nonfibre-forming resin includedifiiculties encountered in dyeing the coating and economic difiicultiesassociated with the manufacture of such fibres.

It is an object of the present invention to provide v bonded fibrousmaterials which have adequate strength but are less stiff and moreattractive to handle than the prior art fabrics, and I have found thatif particular composite -fibres are used as binder fibres then thisobjective is achieved.

Composite fibres containing two or more fibre-forming syntheticpolymeric components, the components extendlice ing along the length ofthe fibres, are known and have been used in fibrous structures. I havenow found that if the components of the composite fibres are chosen sothat at least one but not all of the components are potentiallyadhesive, that it can be rendered adhesive by a treatment which-leavesthe remainder of each fibre substantially unaffected and such fibres areused to form fibrous structures then the potentially adhesive componentsdo not lose their 1 fibrous form on being rendered adhesive underconditions such as to produce an adequately bonded structure. Thepotentially adhesive components remain associated with the remainder ofeach fibre thus producing a structure in which adhesive binder isconfined to small areas where fibres are in contiguous relationship and,since there is no spread of adhesive, the bonded structures are lessstiff and more attractive to handle than prior art fabrics.

Thus according to the present invention, in one of its aspects, there isprovided a bonded textile material of a fibrous character comprising atleast five percent, based on the weight of fibres in the material, ofcomposite fibres substantially free of helical crimp which fibresconsist of at least two fibre-forming synthetic polymeric componentsarranged in distinct zones across the cross-section of each fibre, atleast one but not all of which components is potentially adhesive andlocated in said fibres so as to form at least a portion of theperipheral surface thereof, the fibres in said material being bondedtogether where they are in contiguous relationship by the adhesivecharacteristics of said potentially adhesive component.

According to the present invention, in another of its aspects, there isprovided a process for making bonded textile materials which comprisesforming a fibrous structure containing at least five percent by weightof composite fibres which consist of at least two fibre-formingsynthetic polymeric components arranged in distinct zones across thecross-section of each fibre, at least one but not all of whichcomponents is potentially adhesive and located in said fibres so as toform at least a proportion of the peripheral surface thereof and bondingthe fibres together where they are in contiguous relationship byrendering adhesive the potentially adhesive component of said compositefibres without causing said composite fibres to crimp helically.

For convenience the following discussions will refer to two componentcomposite fibres although it is to be understood that such fibres may,if desired, have more than two components. As used herein the word fibreincludes continuous filaments and staple fibres including flock.

The particular treatment used to elfect bonding depends on whether ornot the composite fibres used possess potential helical crimp. Forinstance, if the components of the composite fibres are arranged in asymmetrical sheathcore relationship then the fibres may not possesspotential helical crimp and it will not be necessary to preventpotential crimp from being developed during bonding. If, for instance,the components are arranged in a non-symmetrical sheath-corerelationship or side-by-side or if the fibres are non-circular, e.g.trilobal, with'the components having a non-symmetrical relationship e.g.one or two of the lobes being formed by the potentially adhesivecomponent, then the fibres may possess potential helical crimp and it isnecessary to prevent such crimp from being developed during the bondingoperation. The development of helical crimp in the composite fibres canbe prevented by subjecting the structure to a restraining pressure, forinstance by using plates or rolls or belts, during bonding, a pressureof about gm./cm. generally being sufficient. Of

course fibres'not possessing potential crimp maystill be subjected topressure during bonding in order to increase the amount of bonding.

The composite fibre structures can be subjected to a variety oftreatments to render adhesive the potentially adhesive component and theparticular treatment used in any particular instance depends, to a largeextent, on the in which the poly-epsilon caprolactam component has thelower softening point, poly(omega-aminoundecanoic acid)lpolyhexamethylene adipamide (nylon 11/66) fibres in which thepoly(omega-aminoundecanoic acid) component has the lower softening pointand polyhexamethylene adipamidelpolyhexamethylene adipamide poly-epsiloncaprolactam copolymer (nylon 66/ 66/ 6) fibres in which the copolymercomponent has the lower softening point.

When the potentially adhesive component is heat activatable and thecomposite fibres do not possess potential helical crimp, suitabletreatments for rendering adhesive the potentially adhesive component andbonding the fibres in the structure together include those not utilizingthe application of pressure for example the use of dry heat such asin ahot air oven or in a radiant heater or the use of a hot liquid media orsteam either superheated or saturated.

When the potentially adhesive component is heat activatable and thecomposite fibres possess potential helical crimp suitable treatments forrendering adhesive the potentially adhesive component and bonding fibresin the structure together include, for example, subjecting: the

' fibrous structure to the application of heat and pressure,

as by pressing the structure between heated plates or by passing itthrough heated calender rolls or by treating the structure while underpressure with a hot liquid media (e.g. hot or boiling water) or steameither superheated or saturated.

When the potentially adhesive component is such that it can be-activatedby a chemical treatment, activation and bonding can be achieved bysubjecting the fibrous structure to a suitable chemical action with orwithout the application of pressure depending on the composite fibresused. An example of such a composite fibre is one consisting, forexample, of various proportions by weight (for example equal quantities)of polyhexamethylene adipamide as one component and a random copolymer(for example an 80:20 copolymer) of polyhexamethyleneadipamide/poly-epsilon 'caprolactam as the other compponent. Thecopolymer component in such composite fibres can be activated i.e.rendered adhesive by treating the fibrous structure with a hot (100 fnon-aqueous, for example, ethylene glycol, solution of formaldehyde,under conditions which leave the polyhexamethylene adipamidecomponent ofthe composite fibres substantially non-adhesive. Alternatively, thecopolymer component may be activated by treating the fibrous structurein a bath of nitric acid of a suitable strength. After bonding thechemical media employed for activating the potentially adhesivecomponent is removed by any suitable means such, for example, asevaporation or washing i with a liquid miscible with the aforementionedchemical media but inert towards fibres in the fibrous structure.

Suitable components for producing the composite-fibres can be found inall groups of synthetic fibre-forming i materials. Because of theircommercial availability, ease of processing and excellent properties,the condensation polymers, for example, polyamides, and polyesters, .andparticularly those which can be melt spun are very suitable for use inthe present invention. Other composite C.) essentially fibres which maybe used include, for example, those based onor containingpolyesteramides, polysulphona- Potentially adhesive componentPolyhexamethyleiie adipamide. Poly(omegaraminoundeeanoie aci DoPolyhexarnethylene adipamlde and poyi-epsilon-caprolactarn copclyemr(various proportions of thgttwo components by weig D0 .L.Polyhexamethyleno adipamide and polyhexamethylene sebaear mlde copolymer(various proportions of the two components by weight). v copolymer(various roportions by weight) of polyet yleneterephthalate andpolypropylene- Polyethyleneterephthalate A terephthalate. PolypropylenePolyethylene. Poly exarnethylene adipamide. A su table polyurethane.Polyethyleneterephthalate A suitable polyethsr-polyurethane copolymer.

Such composite fibres hold their shape and retain their identity asfibres during activation of the potentially adhesive component by virtueof the fact that the other component of the fibres is relativelyunaffected by the activation treatment.

A number of methods are available by which the composite fibres may beprepared. Thus, for example, they may be prepared by the methodsdescribed in British Pats. Nos. 579,081, 580,764, and 580,941 whichinvolve cospinning by a process of melt, plasticised melt, wet or dryspinning, the polymer materials so that they form a unitary filament.Suitable processes and apparatuses for use in the production ofcomposite fibres in which the components are in a side-by-siderelationship by melt spinning, are, for example, described in thespecifications of our British Pats. Nos. 953,379 and 1,035,908. Prior toor during the spinning operation there may be added pigments,plasticisers, dyes, moth-proofing agents, fire-proofing agents, fillers,abrasive and/or light stabilisers. In particular when the potentiallyadhesive component is heat-activatable it may be desirable to add to thespinning solution or otherwise incorporate into the potentially adhesivecomponent suitable substances for lowering the softening point of thatcomponent, such, for example, as plasticisers, soft resins and the like.Among suitable plasticisers for this purpose are dibutyl tartrate, ethylphthallate, and ethyl glycollate. Examples of suitable soft resins arepolyvinyl acetate, ester gum coumarone resin and the lower molecularweight alkyd resins.

It is only necessary that the fibrous structure and the bonded textilematerial derived therefrom composise 5 percent composite fibrescontaining a potentially adhesive component, although I prefer suchfibres to be present in an amount of 10 percent or more, and otherfibres which are inert or substantially so to the activation treatmentto which the fibrous structure is subjected may be employed as a blendwith such composite fibres. Depending upon the particular desiderata inthe bonded textile material to be produced, the percentage of compositefibres containing a potentially adhesive compound present in the fibrouswas and the bonded textile material derived therefrom may be variedwidely.

The composite fibres either in the form of continuous filaments orstaple fibre including flock, may be associated with other fibres orcontinuous filaments of almost any sort, the only substantial limitationbeing that those other fibres must be inert to the treatment renderingadhesive the potentially adhesive component. Wool, silk, flax, cotton,regenerated cellulose, mineral fibres including ass bestos and rockwool, glass fibres, synthetic polymeric fibres (for example, polyamideand polyethyleneterephthalate fibres), other composite fibres and thelike are examples of such fibres which may in a particular instance besuitable. For the purposes of this specification and appended claims weterm such fibres non-activatable fibres.

The fibrous structures containing the composite fibres may be utilisedin the textile art in numerous ways and the structures may take variousforms depending upon the particular bonded textile material desired.

Thus, in the preparation of a woven or knitted fabric the compositefibres either alone or in admixture with non-activatable fibres may becarded and then subjected to drafting and spinning to produce a yarn.The yarn after it has been woven or knitted is then treated to renderadhesive the potentially adhesive component. This treatment serves notonly to stabilise the structure of the yarns within the woven or knittedfabric but also to stabilise the structure of the fabric as a whole byadhesion of fibres at points of inter-crossing of the Weft and warp orof loops in the knitted fabric. In continuous filament form thecomposite fibres containing a potentially adhesive component may befabricated into cords by plying, after which the plies may be bondedtogether.

Besides mixing filaments of relatively short lengths such as staplefibres in the manner contemplated in the descriptions hereinabove, theyarns may be formed of continuous filaments some or all of which arecomposite fibres and such yarns maybe formed into wovenor knitted orplied fabrics in the same manner as a staple fibre yarn.

Utilisation of composite fibres in this manner affords textile fabricsof a knitted, woven or plied character wherein the tendency of thecomponent yarns and filaments to slip with respect to the others isvirtually elimi nated but where fabric drape and handle is notsacrificed. Knitted fabrics, for example, are thus free of any tendencyto ladder when one of the knitted loops therein is broken.

Yarns consisting of or containing composite fibres may be. utilised inthe manufacture of laid or woven scrims which are employed, for example,for the reinforcement of sheets of plastic. The use of composite fibresin the making of scrims greatly simplifies the manufacturing operation.For example, bonding of the laid or woven structure can be accomplishedsimply by the application of heat and pressure and thus the necessityfor using a heat sensitive warp size or dipping the structure in anadhesive before bonding on the loom is eliminated.

In a particularly useful embodiment of this invention the fibrousstructures in the form of fibrous webs are employed in the production ofnonwoven fabrics.

The fibrous web from which the nonwoven fabrics are derived may beprepared by a variety of methods, and the method selected in aparticular instance, depends to a very large extent on the length of thefibres when fibres other than continuous filaments are used.

Staple fibre webs may be prepared, for example, by a Woollen or cottoncarding machine or a garnetting machine which result in a web in whichthe staple fibres are oriented predominately in one direction. The thinweb obtained from a single card or garnet may be used by itself butsometimes it is necessary and desirable to superimpose a plurality ofsuch webs to build up the web to a sufiicient thickness and uniformityfor the end use intended. In building up such a web, alternate layers ofcarded webs may be disposed with their fibre orientation directionsdisposed at a certain angle, convenient y 90, with respect tointervening layers. Such cross-laid webs have the advantage ofpossessing approximately the same strength in at least two directions.Furthermore cross lapping in this manner provides a product having abalanced stretchability. Random or isotropic staple fibre webs may beobtained, for example, by air-laying staple fibres. Thus, one staplefibre web suitable for use in the process of this invention may beobtained by feeding continuous filaments to a cutter or breaker whichdischarges the fibres into an air stream produced by the blower.Suitable conduits are provided to guide a suspension of the staplefibres in a current of air to a foraminous surface on which the fibressettle as an interlaced and matted layer preferably being encouraged todo so by the application of suction on the other side of said surface.The foraminous surface can be in the form of an endless belt which iscaused to travel past the place at which the fibres are fed .to it, soas to form a continuous layer of indefinite length. Instead of having atravelling flat screen, a stationary formed screen may be used for theformation of shaped articles. For example, it may take the form of ahat-shaped cone such as is used in the hatting trade. Alternatively, itmay have any other form suitable for producing the desired shape of thebonded nonwoven fabric of this invention. A method of making a webcontaining fibres of a shorter length, say 0.5 inch or shorter,

them onto a collecting surface where they accumulate in overlappinglayers, the individual filaments in each layer being predominantlycoplanar, lying parallel or substantially parallel to the collectingsurface and to the bottom and top of the web so formed.

Conveniently, the step of web formation is accomplished by mechanicalmeans, such as forwarding jets,

which may be operated to lay the filaments down at random or in somedesired pattern. The collecting surface may be rotated or oscillate toproduce even accumulation of the filaments, and amoving belt may be usedas the collecting surface and in one embodiment of this'inventiondescribed more fully hereinafter the continuous filament web is laiddirectly onto a moving belt.

A convenient method for preparing a continuous filament web in which thefilaments are multifilaments is disclosed in British Pat. No. 1,088,931.

If desired the fibrous web maybe needle-punched on a conventional needleloom and/or a light woven scrim may be incorporated therein.

As stated hereinbefore the bonded structures of the present inventionhave advantages in terms of drape and handle over prior art structuresand this is particularly the case with non-woven fabrics. Thus for agiven fabric strength fabric densities can be much reducedwith-consequent improvements in drape whilst the absence of any binderspread also improves the handle of the fabrics. The advantages can beclearly seen from the accompanying drawings wherein;

FIG. 1 is a graph comparing physical characteristics'of a bonded textilematerial of this invention with those of a prior art bonded textilematerial;

FIG. 2 is a photomicrograph illustrating the effect of heat and pressureon, and the type of bond formed by, the composite fibres of thisinvention;

FIG. 3 is a photomicrograph illustrating the effect of heat and pressureon fibres used in the manufacture f prior art bonded textile materials;

FIGS. 4A and 4B are enlarged schematic representatrons of microscopicobservations of the effect of heat and pressure on fibres used in themanufacture of prior art bonded textile materials; and

FIG. 5 is a photomicrograph of a fragmentary section of a nonwovenfabric according to one embodiment of this inventlon.

The superior properties of the nonwoven fabrics derived from compositefibres is clearly illustrated in the graph shown in FIG. 1 of theaccompanying drawing wherein tensile strength in kg./gm./cm. is plottedagainst density in gm./cm. and which is based on measurements of thetensile strength at various densities of two nonwoven fabrics, one ofwhich was derived from a fibrous web of polyhexamethyleneadipamide/poly(omega-aminoundecanoic acid) composite fibres, thecomponents being arranged side-by-side and the other from a fibrous webwhich comprised a blend of polyhexamethylene adipamide fibres andpoly(omega-- aminoundecanoic acid) fibres the latter fibres beingpresent in amount by weight equivalent to the amount of composite fibresin the outer web and each web being activated and bonded by heatingunder pressure to prevent crimping of the composite fibres Thephotomicrographs of FIGS. 2 and 3 and the diagrammatic representationsof FIGS. 4A and 4B in the accompanying drawings permit a comparison ofthe effect of heat activation and pressure on, and the type of bondformed by, composite fibres and the thermoplastic fibre binders of theprior art.

Referring to FIG. 2, the photomicrograph shows the type of bond formedat a temperature of 240 C. and under pressure between two compositefibres 11 and 12 in the form of twelve denier staple, each consisting oftwo components 13 and 14 arranged in a side-by-side relationship.Component 13 is polyhexamethylene adipamide while component 14, thepotentially adhesive component, is polyepsilon caprolactam. From thefigure, it can be seen that the uncrimped composite fibres 11 and 12 arebonded to one another at cross-over point 15 by a spot bond 16 whichresults from the adhesive characteristics of the polyepsilon caprolactamcomponent of each composite fibre developed by heat. The bond alsoexhibits a high degree of self-bonding, by which I mean that, at thecross-over point 15, the polyepsilon caprolactam component of onecomposite fibre traverses the polyhexamethylene adipamide component ofthe other and fuses with the polyepsilon caprolactam component of thatother composite fibre. It will be observed that, despite the temperatureand pressure conditions to which the composite fibres are subjected, thepolyepsilon caprolactam component 14 remains in contiguous associationwith the polyhexamethylene adipamide component 13 and the open spaces 17between the filaments are characterised by the absence of anypotentially adhesive component.

FIGS. 3 and 4A and 4B illustrate the effect of heat and pressure onfibres which constitute the fibrous web used -in the manufacture of thenonwoven fabrics described -240 C. under pressure. In thephotomicrograph of FIG. 3, which shows in isolation two fibres from theheated and pressed fibrous web, reference numeral 18 designates a 6denier polyhexamethylene adipamide staple fibre and reference number 19a 12 denier polyepsilon caprolactam staple fibre. Under the conditionsof temperature and pressure to which the fibres are subjected, thepolyepsilon caprolactam fibre melts, loses its shape and identity as afibre and forms blobs. The commencement of the deformation of thepolyepsilon caprolactam fibre 19 in this manner is shown in thephotomicrograph wherein the blobs are designated by the referencenumeral 20.

FIGS. 4A and 4B are schematic representations of microscopicobservations of the effect of temperature and pressure on the fibrousweb described in Britist Pat. No. 887,906. In FIG. 4A which shows thebehavior of the fibres at a temperature of approximately 200 C. andunder a moderate pressure, reference numeral 21 designatespolyhexamethylene adipamide fibres and 22 a polyepsilon caprolactamfibre. It will be observed that the polyepsilon caprolactam has retainedits identity as a fibre but I shows the behavior of the fibres at atemperature of approximately 250 C. under a moderate pressure and it canbe seen that the polyepsilon caprolactam fibre has melted, lost itsfibrous shape and identity, and flowed along the polyhexamethyleneadipamide fibres 21 to form numerous blobs 24. At somewhat highertemperatures the polyepsilon caprolactam, as the molten polymer, spreadsfreely through the interstitial spaces in the fibrous web, forming blobsof polymer through the structure.

The difference in behavior on heating and pressing between fibrous webscontaining composite fibres and those prior are fibrous webs containingthermoplastic binder fibres (for example the fibrous web utilised inBritish Pat. No. 887,906) is reflected, at a subjective level, in thehandle and general appearance of the nonwoven fabrics derived from thosewebs. Thus, the nonwoven fabrics de rived from the fibrous websdescribed in the specification of the aforementioned British patent andprepared by the process disclosed therein possess, on account of thepresence of numerous blobs of molten polymer throughout the sturcture, amore or less harsh handle and are frequently palpably rough. Thenonwoven fabrics of my invention frequently have a softer and betterdeveloped textile-like handle.

The photomicrograph of FIG. 5 in the accompanying drawings shows aportion of the fabric derived from a carded web consisting of 10 percentby weight of two inch 12 denier per filament staple fibres formed fromcomposite fibres consisting of equal proportions by weight ofpolyhexamethylene adipamide and an /20 random copolymer ofpolyhexamethylene adipamide/polyepsilon caprolactam, the two componentsbeing arranged in a side-by-side relationship, and percent by weight oneand half inch 3 denier non-activatable polyhexamethylene adipamidestable fibers. The carded web had been placed between two metal platesand maintained at a temperature of 220 C. and subjected to a pressure of30 kg./cm. for a period of approximately one minute to prevent crimpingwhilst effecting bonding.

Under these conditions of temperature and pressure the adhesivecharacteristics of the copolymer component 26 of the composite fibre 25were developed and refined were formed between that component and thenon-activatable polyhexamethylene adipamide fibres 28 at the points ofcontact 29. Despite the activation and bonding treatments to which theweb was subjected the copolymer component remains in contiguousassociation with the polyhexarnethylene adipamide component 27 whichretained its fibrous form. The absence of any spread of the potentiallyadhesive component throughout the structure and the refined nature ofthe bonds formed results in preservation of substantially all theinterstitial spaces 30 between fibres.

The fabric had an excellent tensile strength, a useful porosity, asmooth and pleasant handle and surfaces which were free fromirregularities due to blob formation.

The nonwoven fabrics of this invention have a wide range of appearancesand properties ranging from crisp paper-like structures to drapablefabric-like, or hard boardlike to more bulky felt-like structures. Thedensity and porosity of the fabrics is controlled by the pressure if anyunder which they are formed, and as a general rule, the higher thepressure-the harder and less porous the fabric.

The nonwoven fabrics have a wide range of uses. As examples of some ofthese uses there may be mentioned their use as an industrial fabric inheat, sound and electrical insulation, as floor-coverings, in thefiltration of gases and liquids, as apparel fabrics in the manufactureof hats, caps, jackets and other articles of clothing and asinterlinings for suits and coats, and as household fabrics, for avariety of upholstery purposes. They may also be used as a base to whichvarious coating compositions may be applied to form sheet or shapedmaterials of improved properties.

Some of the bonded textile materials provided by this invention and theprocess for manufacturing them will now be illustrated in the followingexamples which are not to be regarded as in any way limitative of thescope of the invention.

' EXAMPLE 1 A quantity of one and a half inch 12 denier stable fibreformed from oriented polyhexamethylene adipamide/poly(omega-aminoundecanoic acid) (nylon 66/11) composite fibres in whichthe two components were present in equal proportions by weight and in aside-by-side relationship, was carded into a loose fibrous web which wasthen placed between heated platens maintained at 210- 220 C. andsubjected to a pressure of 700 gm./cm. for seconds. The resulting fabricin which the composite fibres were not helically crimped resemble a feltin appearance, had a useful textile-like handle, was free from blobs andpossessedconsiderable strength. A blend of equal proportions by weightof one and half inch 6 denier stable fibres of polyhexamethyleneadipamide and poly- (omega-aminoundecanoic acid) was carded into a looseweb identical to that obtained with the composite fibres and wassubjected to the same bonding treatment. The

' nonwoven fabric derived from this fibrous web had a harsh and hardhandle, and was palpably rough due to the presence of numerous blobsresulting from deformation of the poly(omega-aminoundecanoic acid)fibres. The strength of the two fabrics was determined in an InstronTensile Tester by clamping a two inch wide sample between the jaws ofthe tester'which were set five cms. apart and elongating the sample at arate of 10 cm./min. i.e. 200 percent per minute at a temperature of 21C. and a relatively humidity of 60 percent. The strengths and otherphysical properties of the two fabrics are shown in the table below:

Weight per unit Break- Exten- Density length of ing slon to Tensile offabric fabric, load, break stren th, Sample gm./em. gm./em. kg. percentkgJgmJ cm Composite fibre 0. 31 0. 054 32 28 592 Blend 0. 41 0. 053 2936 548 The nonwoven fabric formed from the composite fibres wastherefore stronger for a given density than the fabric formed from theblend of filaments.

EXAMPLE 2 Th process of Example 1 was repeated except that the webs weresubjected'to a pressure of 2x10 gm./cm. for seconds. The fabric formedfrom the composite fibres was harder and less porous than the obtainedin Example 1. Details of the strength and other physical propertiespossessed by the fabrics are given below:

In this instance the fabric formed from the composite fibres were some34 percent stronger than that obtained from the blended staple and ithad a better developed textile-like handle and appearance.

1O EXAMPLE 3 Continuous filaments consisting ofequal proportions byweight of polyhexamethylene adipamide and an /20 random copolymer ofpolyhexamethylene adipamide/ polyepsilon caprolactam (nylon 66/ 66/ 6)the two components being arranged in a side-by-side relationship werelaid into a web having a weight of 5 ounces per square yard :by thespraying technique described in our British Pat. No. 1,088,931.

A six inch square portion of this web was placed between two pieces of18 mesh brass gauze maintained at temperature of approximately 220-230C. and subjected to a pressure of 5 kgms./cm. for a period of twominutes..The product was bonded nonwoven fabric in which the compositefibres were not helically crimped possessing a textile-like handle and auseful drape or flexibility with the pattern of the gauge embossed onthe surfaces which were free from blob formation. As regards appearancethe product was somewhat similar to a coarse woven fabric.

The strength of the fabric in the longitudinal and transverse directionswas measured on samples 6 inches long and 2 cms. wide, which wereclamped between the jaws of an Instron Tensile Tester, the jaws of whichwere set 5 cms. apart. The samples were elongated at a rate of 5ems/min. i.e. percent per minute at a temperature of 21 C. and arelative humidity of 60 percent.

Details of the strength and other physical properties possessed by thefabric are listed in the table below:

Denisty, gmJcm. 0.28 Weight per unit length, gm./cm 0.0408 Breakingload, kg 9.1 Extension to break, percent 91 Tensile strength,kg./gm./cm. 223

EXAMPLE 4 Continuous filaments consisting of equal proportions by weightof polyhexamethylene adipamide and po1y(omegaaminoundecanoic acid)(nylon 66/11) the two components being arranged in a side-by-siderelationship were laid into a web having a weight of 6 ounces per squareyard by the spraying technique described in British Pat. No. 1,088,931.A portion of this web was placed between two flat aluminium sheets, thecontacting surfaces of which were coated with polytetrafluoroethylene,maintained at a temperature of 210 C. and subjected to a pressure of 21kgms./cm. for'a period of one minute. The product had the smooth surfaceand general appearance of a paper sheet, to which it also had anafiinity in respect of handle and the composite fibres contained nohelical crimp. Its drapable and crease-resistant character made it verysuitable for use as a coat or suiting interliner. Various properties ofthe sheet were then determined on a sample thereof. The tensile strengthin this and the following examples was measured by the procedureoutlined in Example 3 above. Details of the measurements and propertiesare listed in the table belows:

Density, gm./cm. 0.80

Weight per unit length, gm./cm. 0.0374 Break load, kg. 13.5 Extension tobreak, percent 46 Tensile strength, kg./gm./cm. 361

EXAMPLE 5 staple in a Dorstling flock cutting machine. A ten gm.

quantity of this staple was dispersed, by vigorous agitamaintained at atemperature of 230 C. and subjected to a pressure of 27 kgs./cm. for aperiod of one minute, to give a fabric having the appearance and crisphandle of a smooth paper sheet in which the composite fibres had nohelical crimp. The fabric had a density of 0.25 gm./cm. and a tensilestrength of 450 kgs./gm./cm.

EXAMPLE 6 A quantity of two and a half inch 6 denier staple fibre formedfrom composite fibres consisting of equal proportions by weight ofpolyhexamethylene adipamide and an 80/20 random copolymer ofpolyhexamethylene adipamide/polyepsilon caprolactam (nylon 66//66/6),the two components being arranged in a side-by-side relationship, wascarded on a Shirley miniature carder and the laps so formed laid on topof each other with successive laps disposed at an angle of 90 withrespect to the previous lap so forming a cross-laid web having a weightof ounces per square yard. The web was then placed between two twentymesh zinc gauzes maintained at atemperature of 235 C. and subjected to apressure of 40 kgs/cm. for a period of two minutes. The product wasstrong and resilient with the general appearance of a hard thick feltand in which the composite fibres had no helical crimp. The gauzepattern was reproduced on the surfaces of the product to give adecorative effect.

A sample of the sheet had the following properties:

Density, gm./cm. 0.45 Weight per unit length, gm./cm. 0.126 Breakingload, kg. 66.0 Extension to break, percent 8 Tensile strength, kg./gm./cm. 524

EXAMPLE 7 A quantity of two and a quarter inch 6 denier staple fibresformed from composite fibres consisting of equal proportions by weightof polyhexamethylene adipamide and poly (omega-aminoundecanoic acid)(nylon 66/ 11) components arranged in a side-by-side manner was blendedwith a quantity of non-activatable polyhexaethylene adipamide two inch 3denier staple fibres in a 60/40 ratio by weight. A portion of this blendwas thereafter carded using a Shirley miniature carder and the laps soformed laid on top of each other with successive laps disposed at anangle of 90 with respect to the previous lap so forming a cross-laid webhaving a weight of approximately 12 ounces per square yard. The web wasthen placed between two aluminium plates, the contact surfaces of whichwere coated with polytetrafiuoroethylene, maintained at a temperature of230 C. and subjected to a pressure of 40 kgsjcm. for a period of 1minutes. The resulting self-supporting sheet had a smooth surfacesubstantially free from any irregularities due to blob formation, wasflexible enough to have a useful drape and good crease-resistanceproperties. It had a softer handle and a greater porosity than a sheetderived from fibrous web containing 100 percent com- 12 posite fibresand its composite fibres had no helical crimp. Various properties ofthis sheet were then determined on a sample 6 cm. long and 2 cm. wideand the results are listed in the following table:

Density, gm./cm. 0.35

Weight per unit length, gin/cm. 0.0647

Load to break, kg. 36.7

Extension to break, percent 6 Tensile strength, kg./gm./cm. 567

EXAMPLE 8 A quantity of two inch 6 denier staple fibres having the samecomposition as those used in Example 6 was carded on a Shirley miniaturecarder and the laps so formed cross-laid to give a web having a weightof 14 ounces per square yard. The web was then placed between two 4 meshzinc gauzes maintained at a temperature of 230 C. and subjected to apressure of 30 kg. for a period of 1 minute. The product was aself-supporting patterned fabric in sheet form in which the compositefibres had no helical crimp and which had the following properties:

Density, gm./cm. 0.13 Weight per unit length, gm./cm. 0.0276 Breakingload, kg. 8.1 Extension to break, percent 4 Tensile strength,kg./gm./cm. 294

EXAMPLE 9 15 gms. of two inch 3 denier staple fibres, white in colourand formed of composite fibres consisting of equal proportions by weightof polyhexarnethylene adipamide and an /20 random copolymer ofpolyhexamethylene adipamide and polyepsilon caprolactam, the twocomponents being arranged in a side-by-side relationship was blendedwith 15 gms. 3 denier polyhexarnethylene adipamide staple fibres. Of the15 gms. of the non-activatable polyhexamethylene adipamide staplefibres, 6 gms. were coloured yellow, 3 gms. orange, 3 gms. green, 2 gms.red and 1 gm. blue. The blend was then carded using a Shirley miniaturecarder to form a fibrous web. A portion of this web was placed betweentwo 20 mesh zinc gauzes maintained at a-temperature of 230 C. andsubjected to a pressure of 20 kgs/cmfi. for a period of 1 minute. Theproduct resulting from this activation and bonding treatment was anonwoven fabric having pleasant and decorative random coloured effectsand an appearance which was similar in many respects to a coarse wovenfabric the constituent composite fibres being free from helical crimp.The product was eminently suitable for use as an upholstery fabric. Ithad the following properties:

Density, gmJcm. 0.32

Weight per unit length, gm./cm. 0.0236

Breaking load, kg. 13.0

Extension to break, percent 22 Tensile strength, kg./gm./cm. S53

EXAMPLE 10 10 gms. of two inch 6 denier staple fibre formed fromcomposite fibres having the same composition and arrangement ofcomponents as those used in Example 1 were blended with 10 gms. of oneand a half inch cotton staple fibres. The blend was then carded using aShirley miniature carder and the web so formed placed between twoaluminium plates, the contacting surfaces of which were coated withpolytetrafluoroethylene, maintained at a temperature of 215 C. andsubjected to a pressure of 35 kgsJcm. for a period of 1 minute. Theproduct was a nonwoven fabric with the general appearance of a smoothsheet of paper and had a crisp handle the constituent composite fibresbeing free from helical crimp. A number of properties, details of whichare given in table below were then determined on a sample of the fabric:

Tensile strength of this fabric and those produced in Examples 11 to 17which follow was measured along the card direction.

EXAMPLE 11 ing surface of which was coated with polytetrafluoroethylene)and a 20 mesh zinc gauze, maintained at a temperature of 220 C. andsubjected to a pressure of 25 kgs./cm.

for a period of three-quarters of a minute. One surface of the resultingpaper-like fabric was smooth while the other reproduced the pattern ofthe gauze the constituent fibres being free from helical crimp. Thefabric had the following properties:

Density, gm./cm. 0.27

Weight per unit length, gm./cm 0.0169

Breakingload, kg. 3.3

Extension to break, percent 15 Tensile strength, kg./gm./cm. 194

EXAMPLE 12 A quantity of two inch 6 denier staple fibres formed fromcomposite fibres having the same composition and arrangement ofcomponents as in Example 1 was blended with a quantity of two inch 3denier non-activatable polyhexamethylene adipamide staple fibres in a60/40 ratio by weight. A portion of this blend was carded using aShirley miniature carder into a loose fibrous web having a weight ofapproximately 4 ounces per-square yard. A portion of this web was thenplaced between two aluminium plates, the contacting surfaces of whichwere coated with polytetrafiuoroethylene, and heated in a hydraulicpress under a pressure of 28 kgs./cm. for a period of one minute at atemperature of 220 C. A thin paper-like fabric which had the followingproperties was produced, the constituent composite fibres being freefrom helical crimp.

Density, gm./cm. 0.33 Weight per unit length, gm./cm. n 0.0224 Breakingload, kg. 15.7 Extension to break, percent 24 Tensile strength,kg./gm./cm. 704

EXAMPLE 13 A carded web as in Example 12 but composed of 20 percent byweight of the composite fibres and 80 percent by weight of thenon-activatable polyhexamethylene adipamide fibres was heated in ahydraulic press between two 20 mesh zinc gauzes under a pressure of 25kgs./cm. for a period of one minute at a temperature of 225 C Theproduct formed in which the constituent composite fibres were free fromhelical crimp was a fabric having a pleasant, soft textile-like handlewith the general appearance of a somewhat stilt woven fabric. It dyeduniformly with only one dyestuff and was washable. The

fabric was very suitable for use as an interlining fabric. It had thefollowing properties:

Density, gm./cm. 0.21

Weight per unit length, gun/cm. 0.0233

Breaking load, kg. 6.9

Extension to break, percent 20 Tensile strength, kg./gm./cm. 296

EXAMPLE 14 A quantity of two and a half inch. 3 denier staple fibresformed from composite fibres having the same composition and arrangementof components as those of Example 9 was carded using a Shirley miniaturecarder into a loose fibrous web having a weight of 4 ounces per squareyard. A second web having a weight of 4 ounces per square yard wasprepared in a like manner from a blend consisting of equal quantities byweight of the same composite fibres and two inch 3 deniernon-activatable polyhexamethylene adipamide staple fibres. 10 gms. ofthe staple fibres in this web were white, 10 gms. orange, 4 gms. red, 3gms. blue and 3 gms. yellow.

The first web was then laid on top of the coloured web to form acomposite web in which the carded directions of the two webs were thesame. This composite structure was then placed between an aluminiumplate and a 20 mesh zinc gauze maintained at a temperature of 225 C. andsubjected to a pressure of 40 kgs./ 0111. for a period of l /z minutes.

The product was a reversible bi-coloured type fabric with one surfacehaving the appearance and handle of a coarse woven fabric and pleasantlycoloured in a random manner and the other surface essentially white witha smooth and soft handle. The colured surface was basically orange-redflecked with blue. The fabric showed little tendency to delaminate, hada good abrasion resistance and its constituent composite fibres had nohelical crimp. It was very suitable for use as an upholstery fabric. lithad the following properties:

Density, gm./cm. 0.38 Weight per unit length, gm./ cm 0.0542

Breaking load, kg 32.8 Extension to break, percent 36 Tensile strength,kg./gm./cm. 605

EXAMPLE 15 staple fibre formed from polyhexamethylene adipamide and an=/20 random copolymer of polyhexamethylene adipamide and polyepsiloncaprolactam (nylon 66/ 66/ 6) in which the two components were presentin equal proportions by weight and in a side-by-side relationship. Theblend was then carded using a Shirley miniature carder and an 18 inchlong and 12 inch wide portion of the loose. fibrous web formed wasplaced between an aluminium plate (the contacting surface of which wascoated with polytetrafiuoroethylene) and a 20 mesh zinc gauge maintainedat a temperature of 225 C. and subjected to a pressure of 25 kgs./cm.for a period of 1 minute. The product was resilient nonwoven fabric, onesurface of which was patterned and resembled a woven fabric and theother surface was smooth with a soft handle.

The fabric had good abrasion and crease-resistance properties whichrendered it very suitable for use as an interlining fabric and itsconstituent composite fibres had no helical crimp.

Tensile strength, kg./gm./cm.

15 Some of the physical properties possessed by the fabric are listed inthe table which follows:

EXAMPLE 16 A quantity of two inch 12 denier staple fibres formed fromcomposite fibres having the same composition and arrangement ofcomponents as in Example 1' was carded using a Shirley miniature carderinto a loose fibrous web having a Weight of 4 ounces per square yard. A12 inch long, and 9 inch wide portion of this web was then passed at arate of 1 foot per minute between the nip of two calender rollers each 4inches in diameter and which exert a pressure of approximately 10kg./cm. The temperature of the calender rolls was of the order of 240 C.The fabric produced :by this process had the appearance and crisp handleof a smooth paper sheet. It had a porous, relatively open structure andits constituent composite fibres had no helical crimp.

Some of the physical properties possessed by the fabric are listed inthe table which follows:

Density, gm./cm. 0.28 Weight per unit length, gm./cm 0.0248 Breakingload, kg. 7.6 Extension to break, percent 18 EXAMPLE 17 A quantity oftwo and a half inch 3 denier staple fibres formed of composite fibreshaving the same composition and arrangement of components as those usedin Example 1 was blended with a quantity of non-activatablepolyhexamethylene adipamide two inch 3 denier stable fibres in a 60/40ratio by weight. The blended fibres were carded using a Shirleyminiature carder and the laps so formed cross-laid to give a loosefibrous web having a weight of 12 ounces per square yard. A portion ofthis web was then placed between two perforated zinc sheets, theperforations (30 in a square inch) being arranged therein in a regularmanner, maintained at a temperature of 225 C. and subjected to apressure of 30 kgsjcrnl. for a period of 1 minute. During this period,the zinc plates were moved relative to one another over each surface ofthe fibrous web. The surfaces of the nonwoven fabric produced by thisprocess carried interesting and decorative surface eifects. These variedfrom clusters of small rosettes to large hexagonal patterns. Thispatterned effect gave the fabric an appearance not unlike that ofconventional moir fabric.

The fabric which was useful for upholstery purposes had the followingphysical properties and its constituent composite fibres had no helicalcrimp.

' Density, gun/cm. 0.14 'Weight per unit length, gm./cm 0.0180 Breakingload, kg 7.0 Extension to break, percent 19 Tensile strength,kg./gm./cm. 389

EXAMPLE 18 This example and those which follow illustrate methods formaking scrim fabrics from yarns containing continuous composite fibres.

Yarn having a denier of 1610 and containing 117 con tinuous compositefibres consisting of equal proportions by weight of polyhexamethyleneadipamide and an 80/20 random copolymer of polyhexamethylene adipamideand polyepsilon caprolactam arranged side by side and having a breakingload of 9.1 kg. was made up on a wire frame into a woven net-likestructure having 3 ends per inch and 3 picks per inch.

The structure was then placed between two Teflon coated aluminium sheetsand heated in a hydraulic press under a pressure of 10 kgs./cm. at atemperature of 220 C. for a period of 3 minutes.

Under the conditions of temperature and pressure the copolymer componentof the composite fibres was activated and formed bonds at the points ofcontact of the weft and warp yarns, but the composite fibres wasprevented from crimping helically.

The coherent scrim fabric produced was enimently suit able for use as areinforcement material for plastic, for example, polyvinyl chloride,sheets.

' The mean bond strength, measured on the Instron Tensile Tester by theprocedure described in Example 3, was 800 gms. and the fabric had abreaking load of ap proximately 13.4 kgs. per inch.

EXAMPLE 19 proximately 15 kgs. per inch, the composite fibres being freeof helical crimp.

EXAMPLE 20 A net-like fabric was woven with 3 ends per inch and 3 picksper inch from the following yarns:

Warp yarnMultifilamentous yarn consisting of polyhexamethylene adipamideof 1680 denier and containing 272 filaments.

Weft yarn-As the yarn in Example 18.

The woven structure was placed between two Teflon coated aluminiumsheets and heated in a hydraulic press under a pressure of 30 kgs./cm.at a temperature of 220 C. for a period of 3 minutes.

The resulting bonded scrim fabric had a mean band strength of 61.5 gms.and the breaking load of the fabric in the weft direction wasapproximately 13.8 kg. per inch, the constituent composite fibres beingfree from helical crimp.

EXAMPLE 21 Example 18 was repeated using yarn having a denier of 360 andcontaining 24 continuous composite fibres consisting of equalproportions by weight of polyhexamethylene adipamide and a 60/40 randomcopolymer of polyhexamethylene adipamide and poly-epsilon caprolactam,

EXAMPLE 22 A quantity of two and -a half inch 18 denier staple fibreformed from composite fibres having a concentric coresheath composition,consisting of equal proportions by weight of polyhexamethylene adipamideas core and polyeps ilon caprolactam as sheath was carded on a Shirleyminiature carder and the laps so formed laid on top of each other withsuccessive laps disposed at an angle of with respect to the previous lapto form a cross-laid web having a weight of approximately 10 ounces persquare yard. The web was then treated in an atmosphere of air/ steam, ata temperature of 225 C. for approximately 16 seconds, withoutapplication of pressure to the web. Immediately on leaving the heatingzone the bonded web was subjected to a pressure of about 2 kg/crn. toyield a material having the following properties:

The resulting self-supporting fabric was suitable for A carpet underlay,air filters, interlinings and so on, and its fibres were free of helicalcrimp.

EXAMPLE 23 A quantity of one and a half inch 3 denier staple fibresformed from composite fibres having a concentric coresheath arrangementof components, consisting of 75% by weight of polyhexamethyleneadiparnide (nylon 6.6) as core, and 25% by weight of an 80/20 randomcopolymer of polyhexamethylene adipamide/polyepsilon caprolactam (nylon6.6/ 6) as sheath wasprepared. This was blended with an equal quantityof one and a half inch 3 denier staple fibres of non-activatablepolyhexamethylene adipamide (nylon 6.6). The blend was carded on aShirley miniature carder and the laps so formed laid on top of eachother with successive laps at 90 with respect to the previous lap toform a cross-laid web. The web was treated in an oven at 235 C. for 16seconds as in Example 22 and subjected'to a pressure of 2 kg./cm.immediately on leaving the oven. A self supporting fabric, suitable forinterlinings was formed, in which the fibres had no helical EXAMPLE 24This example illustrates the improved tensile properties of fibrousstructures manufactured from composite fibres containing a potentiallyadhesive component over fibres coated with non-fibre-forming bindermaterial prior to forming the fibrous structure, as known in the priorart.

A web was made from composite symmetrical coreand-sheath continuousfilaments by deposition from an air gun traversing across a movingconveyor. The fila- -ments consisted of 89.5% polyhexamethyleneadiparnide (nylon 66) as core, and 10.5% of a 70/30 random copolymer ofpolyhexamethylene adipamide/polyepsilon caprolactam (nylon 66/ 6). Onefilament of this composite structure was passed through an air guntraversing at 24 cycles per minute with a 30" stroke, at a height of 30"above an earthe d conveyor, which was advancing at 0.2 ft./min.perpendicularly to the direction of traverse of the air gun. In thisfashion a web of composite fibres containing a potentially adhesivecomponent was fabricated, referred to in this Example as Web A.

A second web was made, consisting of 100% polyhexamethylene adiparnide(nylon 66) on to which a solution of non-fibre-forming adhesive wassprayed 9 feet above the traversing air gun. The non-fibre-formingadhesive had the following constituency when sprayed:

Parts Polyvinyl chloride (binder) 100 Dioctyl sebacate (plasticiser) 100Methyl ethyl ketone (solvent) 2000 The filaments so formed were found toconsist of a core of polyhexamethylene adiparnide surrounded by aconcentric sheath of polyvinyl chloride. A web was fabricated using thesame apparatus as the Web A above, and-this web is referred to in thisExample as Web B.

Portions of Web A and Web B were pressed between silicone release papersat 500 lbs./ sq. in. at a temperature of 175 C. for five minutes toeffect interfilamentary bonding in the web, and the resulting bondedstructures were tested for strength.

Breaking Density, Web weight stren th,

Web A" 0. 43 24. 3 280. 0 0. 45 38. 3 20. 5

Web B Web A which was manufactured from composite fibres containing apotentially adhesive component, according to the present invention, wasfound to have considerably greater breaking strength than Web B whichcontained a non-fibre-forming sheath according to the prior art, and thefibres of both webs were substantially free from helical crimp.

I claim:

1. A bonded textile material of a fibrous character comprising at leastfive percent, based on the weight of fibres in the material, ofcomposite fibres substantially free of helical crimp which fibresconsist of at least two fibre-forming synthetic polymer componentsarranged in distinct zones across the cross-section of each fibre, saidcomposite fibres having the ability to form a helical crimp uponactivation of the self-crimping properties of the fibres, at least onebut not all of which components is potentially adhesive and located insaid fibres so as to form at least a portion of the peripheral surfacethereof, the fibres in said material being bonded where they are incontiguous relationship by the adhesive characteristics of saidpotentially adhesive component.

2. A bonded textile material according to claim 1 wherein the materialis in the form of a nonwoven fabric having a density of at least 0.1gm./cm.

3. A bonded textile material according to claim 1 wherein compositefibres are present in an amount of between 20 to percent, based on theweight of the fibres in the material, and the balance, if any, arenonactivatable fibres.

4. A bonded textile material according to claim 3 wherein thenon-activatable fibres are wool, cotton, viscose rayon or syntheticpolymer fibres.

5. A bonded textile material according to claim 1 wherein the compositefibres contain only two components.

' 6. A bonded textile material according to claim 5 wherein the twocomponents of the composite fibres are arranged in a side-by-siderelationship.

7. A bonded textile material according to claim 5 wherein thepotentially adhesive component completely surrounds the other component.

8. A bonded textile material according to claim 5 wherein the componentsare polyamides, polyesters, polyesterarnides, polysulphonamides,polyolefins, polyurethanes or copolymers thereof.

9. A bonded textile material according to claim 8 wherein the twocomponents comprise dillerent polyamides.

10. A bonded textile material according to claim 9 wherein thepotentially adhesive component is poly(omegaaminoundecanoic acid) andthe other component is polyhexamethylene adiparnide.

11. A bonded textile material according to claim 9 wherein thepotentially adhesive component is a copolymer of polyhexamethyleneadiparnide and polyepsilon caprolactam and the other component ispolyhexamethylene adiparnide.

12. A process for making bonded textile materials which comprisesforming a fibrous structure containing at least five percent by weightof composite fibres which consist of at least two fibre-formingsynthetic polymeric components arranged in distinct zones across thecross section of each fibre, said composite fibres having the ability toform a helical crimp upon activation of the selfcrimping properties ofthe fibres, at least one but not 19 all of which components ispotentially adhesive and located in said fibres so as to form at least aproportion of the peripheral surface thereof and bonding the fibrestogether Where they are in contiguous relationship by rendering adhesivethe potentially adhesive component of said composite fibres whilst saidfibrous structure is under a pressure of at least 1 gun/cm. so as toprevent said composite fibres from forming a helical crimp.

13. A process as claimed in claim 12 in which the composite fibres donot possess potential helical crimp and the potentiallyadhesivecomponent is rendered adhesive by heating the structure.

14. A process as claimed in claim 12 in which the potentially adhesivecomponent is rendered adhesive by chemical treatment whilst it is undera pressure of at least 1 gm./cm.

15. A process as claimed in claim 14 in which the chemical treatmentcomprises contacting the fibrous structure with a non-aqueous solutionof formaldehyde.

16. A process as claimed in claim 15 in which the chemical treatmentcomprises contacting the fibrous structure with a nitric acid solution.

References Cited UNITED STATES PATENTS ROBERT F. BURNETT, PrimaryExaminer M. A. LITMAN, Assistant Examiner US. Cl. X.R.

